Flow relaxation is not ATP-mediated in the rabbit ear artery

ATP has been proposed to play a role in flow-induced dilation of blood vessels. Changes in flow would alter the concentration of ATP at lumenal endothelial P2Y receptors, occupation of which results in dilation. We tested the hypothesis that the lumenal release of ATP close its receptors on the endothelium and the subsequent influence of flow rate on its concentration at such receptors acts as a flow sensing system. The effect of the selective P2Y-purinoceptor antagonist reactive blue 2 on relaxation of the isolated rabbit ear resistance artery to flow, ATP and ACh was studied. We found that reactive blue 2 (100 micromol/L) significantly inhibited ATP-induced relaxation, but had no effect on equivalent relaxation induced by intraluminal flow (10-40 microl/min). It reduced ACh-induced relaxation to a less extent. These findings strongly suggest that flow-induced relaxation of the rabbit ear resistance artery can occur without the mediation of locally released ATP.